1. Field of the Invention
The present invention relates to a ceramic heating jig, more specifically to a ceramic heating jig suitably used for a heat treatment process in a process for producing a semiconductor device or an optical device.
2. Description of the Related Art
As a general resistance heating heater used for a process for producing a semiconductor device or the like, there has been conventionally used a heater wherein a wire or a foil made of metal having high melting point such as molybdenum, tungsten (W) or the like is wound around or adhered on a base material made of sintered ceramics such as alumina, aluminum nitride, zirconia, boron nitride, or the like, on which a electrical insulating ceramic plate is placed. As improvement thereof, there have been developed a resistance heating ceramic heater wherein an exothermic layer made of conductive ceramics is provided on an electrical insulating ceramic base material, on which electrical insulating ceramic is coated, and a resistance heating ceramic heater wherein a conductive heating element such as W or the like is buried in electrical insulating ceramic, and is molded integrally. They are improved in insulating property and corrosion resistance.
As a ceramic base material, there is generally used a sintered body wherein a sintering additive is added to a raw material powder, which is then sintered. In such a ceramic base material, damage is caused by thermal stress generated due to a difference of thermal expansion coefficient from heterogeneous material such as a heating element. For example, when semiconductor wafer or the like is placed and heated on a ceramic heater base consisting of heterogeneous material such as a ceramic base material and a heating element, a failure of surface close contact with the wafer may be occurred due to the above-mentioned damage, which may cause disorder of temperature distribution.
As a method for suppressing such damage, there have been proposed, a method of increasing stiffness by increasing thickness of ceramic base material, and a method of reinforcing fixing with a table. However, if a damage is suppressed by methods described above, thermal stress may be concentrated inside of ceramic base material, and on an interface between a ceramic base material and a heating element. Accordingly, if temperature is increased and decreased repeatedly, problems such as breakage at sintered grain boundary or an interface between a ceramic base material and a heating element may be caused.
Furthermore, if thickness of a ceramic base material is increased, thermal capacity is increased, and thus there may be caused a problem that it takes long time to raise and lower a temperature.
In order to solve the problem, there have been developed a multi-layer resistance heating ceramic heater that is an integral type wherein a heater pattern consisting of pyrolytic graphite film formed by thermal chemical vapor deposition method (thermal CVD method) is joined on a surface of a supporting substrate consisting of pyrolytic boron nitride film formed by thermal CVD method, and the heater pattern is covered with a close layered protective film made of the same material as that of the supporting substrate, namely pyrolytic boron nitride.
The multi-layer resistance heating ceramic heater has a high purity and is chemically stable and strong to thermal shock. Accordingly, it has been used in various fields that requires rapid raising and lowering of temperature. For example, it has been used in a field of production of a semiconductor wafer. Specifically, it is used widely at a continuous process wherein a semiconductor wafer or the like is treated in a single wafer processing method, and temperature is changed in phase. Since the multi-layer ceramic heater is totally manufactured by a CVD method as described above, there is no grain boundary, and thus there is no de-gassing, so that there is no harmful influence to the process when heating is conducted in a vacuum process. Accordingly, it has been used in a wider field.
However, pyrolytic boron nitride constituting the above-mentioned multi-layer ceramic heater has a small Young""s modulus, a warp is caused during heating due to thermal stress remaining in the substrate during production. If a wafer or the like is placed and heated directly thereon, failure of surface close contact may be caused, which may cause disorder in temperature distribution. Accordingly, it is necessary that susceptor made of material that has large Young""s modulus and is excellent in heat resistance is located on the ceramic heater, and the wafer is placed thereon to be heated.
A susceptor has a thermal capacity corresponding to size, and a rate of raising and lowering temperature of a wafer in the case that a wafer is heated on the susceptor depends on thermal capacity of the susceptor. The rate of raising and lowering temperature can be increased by decreasing thermal capacity of a susceptor. In that case, it is necessary to decrease thermal capacity by decreasing thickness of the susceptor, since it is necessary to make an area of upper surface thereof the same or more as the wafer. If a thin susceptor is used, thermal capacity can be decreased, and a rate of raising and lowering temperature is raised. However, if it is too thin, there may be caused a warp during processing of the susceptor and thermal deformation during raising and lowering temperature, which may lead to disorder of temperature distribution due to failure of surface close contact with a wafer.
In the case that a susceptor is fixed to the ceramic heater or the like by fastening tightly with a screw or a bolt, stress generated around the fixed part when it is fasten, or thermal stress generated during heating may cause swell of the susceptor, which may lead to breakage thereof. As described above, deformation or breakage due to fixing with a screw or a bolt is not only a problem in the susceptor, but also a problem in a part that is especially heated, such as a ceramic heater, a heat shielding plate used for shielding heat of a ceramic heater or the like.
The present invention has been accomplished to solve the above-mentioned problems, and an object of the present invention is to provide a ceramic heating jig wherein defects such as thermal deformation, breakage or the like of susceptor or the like are hardly caused, temperature can be raised or lowered rapidly, and flatness of a susceptor can be kept even at high temperature.
To solve the above-mentioned problems, the present invention relates to a ceramic heating jig consisting of a susceptor on which a work to be heated is placed, a ceramic heater for heating the susceptor and at least one heat shielding plate for shielding heat of the ceramic heater wherein the susceptor and the heat shielding plate are located so that each of them is located across the ceramic heater each leaving a certain space therefrom, a thickness of the susceptor is 0.5 mm to 5 mm, a thickness of the ceramic heater is 0.5 mm to 3 mm, a thickness of the heat shielding plate is 0.5 mm to 3 mm.
As described above, in a ceramic heating jig wherein the susceptor having a certain thickness and at least one heat shielding plate are located so that each of them is located across the ceramic heater each leaving a certain space therefrom, a thickness of the susceptor and the ceramic heater is not too thin, so that strength is sufficient, swell or the like is never caused on the upper surface of the susceptor. They are not too thick either, so that they have small thermal capacity, and can raising and lowering a temperature rapidly.
In that case, it is further preferable that an interval between the susceptor and the ceramic heater, and an interval between the heat shielding plate and the ceramic heater are 0.5 mm to 10 mm.
If the susceptor, the ceramic heater and the heat shielding plate are located leaving such an interval, the intervals between them are not too narrow nor too wide, the heat of the ceramic heater can be conducted to the susceptor efficiently, and emission of the heat to the opposite side to the susceptor can be prevented efficiently.
According to the present invention, a ceramic heating jig consisting of a susceptor on which a work to be heated is placed, a ceramic heater for heating the susceptor and at least one heat shielding plate for shielding heat of the ceramic heater wherein spacers are provided respectively between the susceptor and the ceramic heater, between the heat shielding plate and the ceramic heater, and between the heat shielding plates when more than one heat shielding plates are provided, the susceptor, the ceramic heater and heat shielding plate are held to be integrated by being sandwiched between an elastic means having elasticity contacted with the lower surface of the heat shielding plate that is located at the lowest position and a restraint means contact with the upper surface of the susceptor on which the work is placed for prohibiting action in a vertical direction to the upper surface by the elastic means.
As described above, if spacers are provided between each of the susceptor, the ceramic heater and the heat shielding plate (hereinafter referred to as a heating member occasionally), and the heating members are supported to be integrated by being sandwiched between the elastic means having elasticity and the restraint means, thereby each of the heating members can be expanded without too much force to a direction of thickness and a direction of surface during heating. Accordingly, damage, swell or the like are not generated.
In that case, it is preferable that thickness of each of the heating members are in the above-mentioned range, namely 0.5 mm to 5 mm as for the susceptor, 0.5 mm to 3 mm as for the ceramic heater, 0.5 mm to 3 mm as for the heat shielding plate.
Furthermore, an interval between each of the heating members is also in the above-mentioned range, namely, the interval between the susceptor and the ceramic heater, and the interval between the heat shielding plate and the ceramic heater are 0.5 mm to 10 mm.
As described above, if the heating members having a certain thickness are located at a certain interval via a spacer, and the heating members are held to be integrated by being sandwiched between the elastic means and the restraint means, damage, swell or the like during heating can be efficiently prevented.
Furthermore, it is preferable that the above-mentioned elastic means and restraint means are fixed on the table, and the above-mentioned elastic means comprises spring. According to such a constitution, each of the heating members can be supported to be integrated more stably.
Preferably, a takeout terminal for supply of electricity is provided at the above-mentioned table of the ceramic heating jig of the present invention.
It is more preferable that a thermocouple for controlling temperature and/or for monitoring temperature is provided in the above-mentioned susceptor and/or ceramic heater.
According to such a constitution, electricity can be easily supplied to the ceramic heater and temperature of the susceptor can be accurately controlled.
Furthermore, air supply inlets and air exits are preferably provided in the table. In that case, it is more preferable that air supply inlets are provided at a center of the table, and more than one of the above-mentioned air exits are provided outside the air supply inlets at a peripheral part of the table.
If nitrogen or the like is supplied and exhausted through the above-mentioned air supply inlets and air exits, ventilation of a space in the heating jig between the table and the heat shielding plate can be conducted, and the difference in pressure of the space in the heating jig from a space outside such as a space in a processing room in which the heating jig is installed can be controlled. Furthermore, supplied gas is dispersed in the inner space in the heating jig and exhausted, so that a lowering rate of temperature (a cooling rate) of the heating jig can be improved, and uniform cooling can be achieved.
Then, the above-mentioned spacer is preferably more than one ceramic spacer in a shape of sphere or column.
Such a spacer can advantageously function especially when each of the heating members is expanded.
It is preferable that the above-mentioned restraint means also function as means for defining position of the work to be heated that is placed on the susceptor.
If the restraint means is made to be fit into the shape of the work to be heated, it can also function as a means for positioning the work to be heated, and it is not necessary to provide a positioning means on the susceptor separately, so that the constitution can be simple.
The above-mentioned ceramic heater preferably consists of a complex of a base material made of pyrolytic boron nitride and a heating element made of pyrolytic carbon. Difference in thermal expansion coefficient of each of pyrolytic boron nitride and pyrolytic carbon of the complex is preferably 2xc3x9710xe2x88x926 xc2x0 C. or less.
Such pyrolytic boron nitride and pyrolytic carbon of a complex can be suitably produced according to a thermal chemical vapor deposition method.
Such a complex ceramic heater has good adhesion property, and stress or warp is hardly caused therein.
The above-mentioned susceptor is preferably made of any of aluminum nitride, boron nitride, a complex of aluminum nitride and boron nitride, silicon nitride, silicon carbide, quartz, carbon coated with silicon carbide, carbon coated with pyrolytic boron nitride, or sialon. The heat shielding plate is preferably made of any of aluminum nitride, boron nitride, a complex of aluminum nitride and boron nitride, pyrolytic boron nitride, silicon nitride, silicon carbide, quartz, carbon coated with silicon carbide, carbon coated with pyrolytic boron nitride, carbon coated with pyrolytic carbon, sialon, W, Mo, Ta, inconel or stainless steel.
The above-mentioned restraint means is preferably made of any of aluminum nitride, boron nitride, a complex of aluminum nitride and boron nitride, pyrolytic boron nitride, silicon nitride, silicon carbide, quartz, carbon coated with silicon carbide, carbon coated with pyrolytic boron nitride, carbon coated with pyrolytic carbon or sialon.
The above-mentioned table is preferably made of any of boron nitride, a complex of aluminum nitride and boron nitride, pyrolytic boron nitride, silicon nitride, silicon carbide, quartz, carbon coated with silicon carbide, carbon coated with pyrolytic boron nitride, carbon coated with pyrolytic carbon, sialon, W, Mo, Ta, inconel or stainless steel.
The spring in the above-mentioned elastic means is preferably made of any of carbon fiber reinforced carbon, silicon nitride, W, Mo, Ta, inconel or stainless steel.
If each of the members of the ceramic heating jig of the present invention is made of the above-mentioned material excellent in heat resistance, sure heating treatment can be conducted stably even at high temperature.
As explained above, in the ceramic heating jig of the present invention, a susceptor and a ceramic heater having sufficient strength, not large thermal capacity and an adequate thickness, and a heat shielding plate having sufficient strength and a thickness excellent in heat shielding property are provided at a certain interval in this order. A work to be heated can be heated and cooled rapidly. Each of these heating members can be supported elastically, damage or the like is not occurred on the surface of the susceptor during heating. Accordingly, a semiconductor wafer or the like can be heated uniformly.